1. Field of the Invention
The present invention relates to pumping apparatus. In particular, the present invention relates to an empty supply bag detector for use with volumetric infusion pumps for administration of intravenous (IV) fluids.
2. Description of the Prior Art
To improve health care, there has been considerable effort with regard to the administration of intravenous (IV) fluid. For many years IV solutions were administered only by the force of gravity. The volume rate was measured by counting the number of drops per minute. In many instances this method proved unsatisfactory. Drop size is directly proportional to surface tension, which is affected by viscosity, temperature, type of solution, and also drop size is affected by the speed at which the drop forms. The drop rate is affected by the gravitational force and the restrictions of the tube and needle. If a tube is partly occluded, the drop rate will decrease or as the IV supply decreases the hydrostatic pressure will decrease causing a decrease in drop rate. In many cases, therefore, the variability of both the drop size and the drop rate (both of which are for the most part beyond the control of the operator) makes this method of administration of intravenous fluid unsatisfactory.
Improvements have been made by adding an electronic drop counter together with either a controller or a peristaltic pump. The electronic drop counter and controller combination controls the drop rate but makes no improvements in controlling drop size, and also has the deficiency of not being able to control drop rate if back pressure increases beyond the hydrostatic forcing pressure. The electronic drop counter and peristaltic pump combination increases the forcing pressure but lacks an accurate metering method.
Improvement in metering methods results with the use of displacement pumps, which offer the capability of greater precision in controlling IV flow rates than is possible with the prior art IV controllers which depend on gravity. These pumps, in addition to metering the fluid, also apply positive pressure to the fluid or the IV tubing.
It has been recognized in the prior art that a dangerous condition can occur with volumetric infusion pumps if the supply bag or reservoir becomes empty while the pump continues to operate. The supply bag may become empty due to an improper setup by the medical personnel, or due to a system malfunction during operation of the pump. In either case, it is highly desirable to detect this condition and to stop the operation of the pump.
Several methods have been used in the prior art to detect an empty supply bag. In one system, a drop counter is placed on the drip chamber which is connected to the supply bag. When the bag goes empty, the drops cease, thereby providing an indication of the empty supply bag. This type of system, however, requires that the attending medical personnel connect a drop sensor to the drip chamber. This is a procedure in which setup problems can arise because of water level in the drip chamber, drops splashing, and ambient light.
A second system for detecting an empty supply bag places an air detector in the pump housing. This method, however, typically does not allow for easy removal of air from the pump housing. This leads to complications when a supply bag goes empty and must be replaced by a new bag. The air within the pump must be removed before operation of the pump can again be commenced.
A third system for detecting an empty supply bag includes a pump which detects an occlusion in the supply line between the supply bag and the pump in conjunction with a floating valve located in the drip chamber. This system has the disadvantage that it requires the extra expense of a floating valve in the drip chamber. Since the drip chamber must be part of the disposable portion of the system, the overall cost of the pumping system is increased.
There is a continuing need for a low cost, yet effective pump and empty supply bag detector which is simple to use, permits easy removal of air from the pump when supply bags have changed, and does not increase the cost of the disposable portions of the pumping system.